It's not built-in and not supported by official team working at Krita Foundation. You can find Stable Diffusion as a plugin made by someone externally to the team.
https://github.com/w4ffl35/krita_stable_diffusion
It requires downloading the model of the AI separately, and you'll need an account.
Stable Diffusion/LAION model is not Free/Libre and Open-Source compatible. It's a form of Open-Source with many rules on the top to prevent "AI Take Over" and unethical usage (how ironic).
senooken JP Social is a social network, courtesy of senooken. It runs on GNU social, version 2.0.2-beta0, available under the GNU Affero General Public License.
All senooken JP Social content and data are available under the Creative Commons Attribution 3.0 license.